Hadith 3:116

Narrated Ibn 'Umar:

The Prophet observed the fast on the 10th of Muharram ('Ashura), and
ordered (Muslims) to fast on that day, but when the fasting of the
month of Ramadan was prescribed, the fasting of the 'Ashura' was
abandoned. 'Abdullah did not use to fast on that day unless it
coincided with his routine fasting by chance.